Final answer:
Concentric, eccentric, and isometric/static refer to the three types of muscle contractions: concentric when muscles shorten, eccentric when they lengthen under tension, and isometric when muscles generate force without changing length.
Step-by-step explanation:
Concentric, eccentric, and isometric/static are three major types of muscle contractions in the human body. When discussing muscle tissues, we refer to three major types found in the body: skeletal, smooth, and cardiac muscle. Of the contraction types, concentric contractions involve the muscle shortening to move a load, such as when lifting a hand weight upwards; the muscle fibers' sarcomeres shorten, pulling the actin with myosin heads, decreasing the elbow joint angle as the forearm moves toward the body.
Eccentric contractions occur as the muscle lengthens, controlling the lowering of a hand weight and increasing the elbow joint angle as the amount of cross-bridges decreases. Finally, isometric or static contractions are where the muscle does not change in length but still generates tension; an example would be holding a hand weight steady in mid-air without moving it up or down.
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